The invention relates to a jet engine comprising, from upstream to downstream (the upstream and downstream directions being defined by the direction of circulation of the primary flow), a high-pressure compressor, a diffuser grating and a combustion chamber, said high-pressure compressor comprising an external shell which radially delimits the duct for said primary flow and is connected to an annular structure extending radially outward, said diffuser grating comprising in the axial continuation of said external compressor shell an external casing connected to a rearwardly oriented conical strut delimiting, upstream, the end of said combustion chamber, said strut itself being connected to an external casing shell which extends in the upstream direction and is fastened to said annular structure by fastening means, said strut, said external casing shell and said annular structure defining a cavity around said diffuser grating, air bleed orifices being made in said strut in order to bring the end of the combustion chamber into communication with said cavity, said external casing shell being equipped with outlet vents for the bled air, and sealing means being provided between said annular structure and said external diffuser grating casing in order to isolate said cavity from the duct for the primary flow.